In flight, a pilot navigates their aircraft according to a flight plan that is filed with the ATC authorities. The flight plan may be manually or electronically loaded into the aircraft's Flight Management System (“FMS”) at the beginning of the flight, prior to departure. Among other things, the flight plan typically includes a plurality of geographic waypoints that define a planned track of the aircraft and the specific times at which the aircraft is to arrive at those waypoints. The flight plan may also require that ascent maneuvers, descent maneuvers and turn maneuvers be conducted at some of those waypoints. The flight plan, when associated with aircraft performance information and metereological conditions from aircraft sensors (e.g. fuel burn rates), are used by the FMS or other avionics system (e.g. an electronic flight bag (“EFB”)) to determine important flight performance metrics such as, for example, fuel consumption, environmental impact, estimated times of arrival (“ETA”), and flight overhead costs.
Normally, clearance changes in a flight plan are communicated to an aircraft in flight and may be displayed in the aircraft's Cockpit Display Unit (“CDU”). Exemplary, non-limiting types of a CDU include a Data-link Cockpit Display Unit (“DCDU”) and a Multi-Purpose Cockpit Display Unit. (“MCDU”). Typically, the flight crew reviews the clearance and evaluates the change in the flight plan to determine the impact of the clearance on the aircraft's fuel supply, its ETA and other flight parameters (e.g. speed of advance, crew costs and overhead costs). The pilot then either signals the acceptance of the clearance with a positive or a “Wilco” response, or signals the rejection of the clearance with an “Unable” response. These responses are usually accomplished by manipulating a physical transducer, such as a button or a switch, which is located proximate to an electronically rendered selection label on the CDU or MCDU.
However, in transoceanic flight positive ATC is not effective or even possible because the ATC radar does not reach the aircraft. As such, aircraft traverse oceanic airspace by following certain aircraft separation procedures. The separation procedures limit the ability to make altitude changes even if it desirable and can easily be done. To overcome the limitations allowing altitude changes, In Trail Procedures (“ITP”) have been developed to facilitate desirable altitude changes while preventing close encounters with other aircraft. The ITP are more fully described in RTCA DO-312 entitled “Safety, Performance and Interoperability Requirements Document for the In-Trail Procedure in Oceanic Airspace (ATSA-ITP) Application”, RTCA Incorporated, Washington D.C. (2008) and is herein incorporated by reference its entirety in the interest of brevity. In short, the ITP insures that a minimum distance is maintained from a reference aircraft, while own ship transitions to a new flight level.
During transit, it is a common occurrence for a pilot to want to change altitude for economic, weather or other reasons. However, because of the absence of positive ATC from which to evaluate a change in an aircraft's flight plan during flight, the pilot must personally determine if the flight level change is possible (i.e. likely to be granted by the ATC) under the ITP, and then determine if a flight level change is desirable (e.g. cost and/or time effective). Conventionally, such decisions were made manually from information synthesized from various cockpit information sources.
In order to determine the desirability of changing the flown flight level (i.e. requesting a clearance), a pilot typically runs the original flight plan through the FMS or an EFB to obtain a set of flight parameters based on the original flight plan. The pilot may then key in changes to the flight plan related to the desired flight level. The pilot may process the amended flight plan back through the FMS to obtain a pro form a set of flight parameters. The pilot then manually compares both sets of flight parameters to determine the acceptability of any resulting changes in ETA, changes in fuel consumption, environmental impact, flight overhead costs, etc. The pilot then must manually determine whether the ITP procedures would permit him to make the clearance change. Such procedures may result in significant heads down time during which the pilot's attention may be diverted. Therefore, there is a need to improve the clearance decision process to minimize administrative work load, eliminate heads down time and also not inadvertently miss an opportunity to perform a desirable flight level change.